3,069 research outputs found
Ward identity and electrical conductivity in hot QED
We study the Ward identity for the effective photon-electron vertex summing
the ladder diagrams contributing to the electrical conductivity in hot QED at
leading logarithmic order. It is shown that the Ward identity requires the
inclusion of a new diagram in the integral equation for the vertex that has not
been considered before. The real part of this diagram is subleading and
therefore the final expressions for the electrical conductivity at leading
logarithmic order are not affected.Comment: 25 pages with 5 eps figures, discussion in section 3 improved; to
appear in JHE
How Participation Creates Citizens: Participatory Governance as Performative Practice
Participation is a prominent feature of many decision-making and planning processes. Among its proclaimed benefits is its potential to strengthen public support and involvement. However, participation is also known for having unintended consequences which lead to failures in meeting its objectives. This article takes a critical perspective on participation by discussing how participation may influence the ways in which citizens can become involved. Participation unavoidably involves (1) restrictions about who should be involved and about the space for negotiation, (2) assumptions about what the issue at stake is, and (3) expectations about what the outcome of participation should be and how the participants are expected to behave. This is illustrated by a case study about the Dutch nature area, the Drentsche Aa. The case study demonstrates how the participatory process that took place and the restrictions, assumptions, and expectations that were involved resulted in six forms of citizen involvement, both intended and unintended, which ranged between creativity, passivity, and entrenchment. Based on these findings, the article argues that participation does not merely serve as a neutral place in which citizens are represented, but instead creates different categories of citizens. Recognizing this means reconceiving participation as performative practice. Such a perspective goes beyond overly optimistic views of participation as a technique whose application can be perfected, as well as pessimistic views of participation as repression or domination. Instead, it appreciates both intended and unintended forms of citizen involvement as meaningful and legitimate, and recognizes citizenship as being constituted in interaction in the context of participatio
Beyond the average:Choosing and improving statistical methods to optimize inference from complex neuroscience data
Verhage, M. [Promotor]Sluis, S. van der [Copromotor
Melting Spectral Functions of the Scalar and Vector Mesons in a Holographic QCD Model
We investigate the finite-temperature spectral functions of heavy quarkonia
by using the soft-wall AdS/QCD model. We discuss the scalar, the pseudo-scalar,
the vector, and the axial-vector mesons and compare their qualitative features
of the melting temperature and growing width. We find that the axial-vector
meson melts earlier than the vector meson, while there appears only a slight
difference between the scalar and pseudo-scalar mesons which also melt earlier
than the vector meson.Comment: 27 pages, 10 figure
Beyond complex Langevin equations II: a positive representation of Feynman path integrals directly in the Minkowski time
Recently found positive representation for an arbitrary complex, gaussian
weight is used to construct a statistical formulation of gaussian path
integrals directly in the Minkowski time. The positivity of Minkowski weights
is achieved by doubling the number of real variables. The continuum limit of
the new representation exists only if some of the additional couplings tend to
infinity and are tuned in a specific way. The construction is then successfully
applied to three quantum mechanical examples including a particle in a constant
magnetic field -- a simplest prototype of a Wilson line. Further
generalizations are shortly discussed and an intriguing interpretation of new
variables is alluded to.Comment: 16 pages, 2 figures, references adde
Nonequilibrium time evolution of the spectral function in quantum field theory
Transport or kinetic equations are often derived assuming a quasi-particle
(on-shell) representation of the spectral function. We investigate this
assumption using a three-loop approximation of the 2PI effective action in real
time, without a gradient expansion or on-shell approximation. For a scalar
field in 1+1 dimensions the nonlinear evolution, including the integration over
memory kernels, can be solved numerically. We find that a spectral function
approximately described by a nonzero width emerges dynamically. During the
nonequilibrium time evolution the Wigner transformed spectral function is
slowly varying, even in presence of strong qualitative changes in the effective
particle distribution. These results may be used to make further analytical
progress towards a quantum Boltzmann equation including off-shell effects and a
nonzero width.Comment: 20 pages with 6 eps figures, explanation and references added; to
appear in Phys.Rev.
Oscillatory behavior of the in-medium interparticle potential in hot gauge system with scalar bound states
We investigate the in-medium interparticle potential of hot gauge system with
bound states by employing the QED and scalar QED coupling. At finite
temperature an oscillatory behavior of the potential has been found as well as
its variation in terms of different free parameters. We expect the competition
among the parameters will lead to an appropriate interparticle potential which
could be extended to discuss the fluid properties of QGP with scalar bound
states
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